AAA High Availability Support for Local PPPoX Sessions

This feature enhances the authentication, authorization, and accounting (AAA) capability to meet high availability (HA) criteria
for locally terminated Point-to-Point Protocol (PPP) over Ethernet (PPPoE) and PPPoEoX sessions, where
X represents VLAN or QinQ. The following Feature Manager features are supported in this implementation of AAA HA:

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information,
see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module,
and to see a list of the releases in which each feature is supported, see the feature information table.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature
Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Restrictions for AAA High Availability Support for Local PPPoX Sessions

If an administrator changes the protocol of a server group (for example, from RADIUS to TACACS+), HA will not be available
for sessions configured to use that server group.

IP sessions are not supported in this implementation of AAA HA.

This implementation of AAA HA supports only locally terminated PPPoX sessions, including the following:

Information About AAA High Availability Support for Local PPPoX Sessions

AAA HA Enhancement

Cisco HA delivers carrier grade reliability with Cisco devices running Cisco IOS XE software. Carrier grade means that service
disruption because of outages, service upgrades, or other maintenance activities on Cisco IOS XE platforms are rarely experienced.
To achieve this level of service, Cisco uses two route processors to manage and control the sessions and services for each
device. One processor is active and the other is in standby mode, ready to provide backup. A transition from the active processor
to the standby processor is transparent to the end user, but not necessarily to the service provider.

The router must maintain the following information during transient component failures:

Authentication status of clients

Authorization status

Accounting and billing information

To maintain this information during transitions to the standby processor, Cisco IOS XE software uses an HA replay model to
re-create as much state and database information as possible between the active and standby devices. The HA replay model works
within existing external AAA server protocols to achieve the desired behavior.

HA and Authentication

For authentication, only the following state information is maintained: knowledge that a session authenticated on the active
processor need not be reauthenticated on the standby processor. Each authentication protocol, such as local, TACACS+, or RADIUS,
responds in its protocol-specific way to an authentication request from a standby device. All AAA client authentication replies
on a standby device should be successful.

HA and Authorization

The HA process for authorization data is different from the authentication process. The AAA server caches the authorization
responses for the sessions in order to provide the appropriate authorization attributes to AAA clients during a session replay.
AAA clients use the authorization attributes to create a session copy on the standby route processor.

HA and Accounting

The AAA HA accounting framework takes advantage of existing AAA features such as system accounting and periodic accounting
to limit the loss of accounting and billing information caused by a switchover between an active processor and a standby processor.

System Accounting

System accounting is a separate accounting capability that informs AAA servers about the state of a client device, such as
a router. The AAA server receives a “System-Off” message when a controlled restart takes place on a client device. The message
notifies the AAA server to clear any active sessions being managed for the specified client. When the client restarts and
becomes available for new sessions, the AAA server receives a “System-On” message. The “System-On” message is also sent following
uncontrolled restarts caused by device failures or other events that do not generate a “System-Off” message. In either case,
the AAA server no longer maintains any active sessions for the specified client device. The server bills or accounts for the
sessions prior to the “System-On” message and starts a new session.

AAA’s accounting HA solution does not add any new requirements to system accounting for AAA servers. Any switchover will look
like a very fast, minimally disruptive outage. Although end users do not experience any loss of service during an HA switchover,
AAA servers reset their sessions and restart accounting for all switched-over sessions.

Periodic Accounting

You can use periodic accounting to dynamically update records of session utilization for billing purposes. Periodic accounting
minimizes the loss of usage statistics. HA does not eliminate the need to configure periodic accounting on a device if you
require dynamic usage statistics for billing purposes. To achieve the HA level of reliability, the existing network topology
configuration must be maintained.

How to Configure AAA High Availability Support for Local PPPoX Sessions

Configuring AAA High Availability Support for Local PPPoX Sessions

There are no configuration tasks associated with this feature. If you maintain your network topology for HA, then the AAA
functions automatically participate in the HA feature for locally terminated PPPoX sessions.

Troubleshooting an AAA High Availability Configuration

SUMMARY STEPS

enable

debug aaa redundancy

disable

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enters the privileged EXEC mode.

Enter your password, if prompted to do so.

Step 2

debug aaa redundancy

Example:

Router# debug aaa redundancy

Displays AAA synchronization data for the session synchronization to the standby device.

RFCs

RFC

Title

RFC 3623

Graceful OSPF Restart

RFC 3847

Restart Signaling for Intermediate System to Intermediate System (IS-IS)

RFC 4781

Graceful Restart Mechanism for BGP

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use
these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products
and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

Feature Information for AAA High Availability Support for Local PPPoX Sessions

The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1. Feature Information for AAA HA Support for Local PPPoX Sessions